This invention relates to a process for converting aqueous preparations of washing- and cleaning-active surfactant compounds into storable granules.
Considerable and greatly increasing significance is attributed to the use of oleochemical surfactant compounds in detergents. On the one hand, the principal considerations in this regard are based on the fact that surfactant compounds of this type can be obtained from renewable vegetable and/or animal raw materials. On the other hand, however, crucial significance is attributed in particular to the high ecological compatibility of selected components of this type. One example of such a class of oleochemical surfactant compounds are the known fatty alcohol sulfates which are produced by sulfation of fatty alcohols of vegetable and/or animal origin predominantly containing 10 to 20 carbon atoms in the fatty alcohol molecule and subsequent neutralization to water-soluble salts, more particularly the corresponding alkali metal salts. Of particular practical significance in this regard are the sodium salts of fatty alcohol sulfates which are based on at least predominantly linear fatty alcohols or corresponding fatty alcohol mixtures containing approximately 12 to 18 carbon atoms in the fatty alcohol molecule. Tallow alcohol sulfates (TAS) with predominantly saturated C.sub.16-18 residues in the fatty alcohol are already of considerable importance for the production of laundry detergents, particularly in solid form, although fatty alcohol sulfates (FAS) with a broader C chain length range also have important detergent properties. Thus, C.sub.12-18 fatty alcohol sulfates containing a high percentage of the lower fatty alcohols in this range, for example based on coconut oil or palm kernel oil, are particularly important anionic surfactants for use in detergents. There are numerous disclosures to this effect in the relevant specialist literature, cf. H. Baumann "Neuere Entwicklungen auf dem Gebiet fettchemischer Tenside" Fat Sci. Technol., 92 (1990) 49/50 and the earlier literature cited therein. Similarly, European patent application 342 917 describes detergents in which the anionic surfactants consist predominantly of C.sub.12-18 alkyl sulfates.
The economic synthesis of light-colored FAS-based anionic surfactants is now an established part of technical knowledge. The corresponding surfactant salts are obtained in the form of aqueous preparations with water contents in the range from about 20 to 80% and, more particularly, in the range from about 35 to 60%. Products of this type have a paste-like to cuttable consistency at room temperature, the flowability and pumpability of the pastes being limited or even totally lost for active substance contents of only about 50% by weight, so that considerable problems arise in the subsequent processing of the pastes, particularly during their incorporation in solid mixtures, for example in solid detergents. Accordingly, there has long been a need to provide FAS-based detergent surfactants in dry, more particularly free-flowing form. It is in fact possible to produce free-flowing FAS powders by conventional drying techniques, more particularly by spray drying. However, serious limitations have been discovered in this regard and, above all, call the economy of using FAS surfactants on an industrial scale into question. Tower-dried TAS powder, for example, has a very low apparent density, so that unprofitable conditions prevail in the packaging and marketing of this detergent raw material. However, even at the production stage of the tower powders, questions of safety can necessitate such heavily restricted operation of the tower drying process that practical difficulties arise. Thus, safety studies of tower powders based on TAS or FAS containing 20% or more of active substance show that the spray drying of such formulations is possible on only a very limited scale and, for example, requires tower entry temperatures below 200.degree. C.
Comparable or other difficulties arise in the conversion of aqueous, more particularly paste-form, preparations of many other washing- and cleaning-active surfactant compounds into storable dry products. Further examples of anionic oleochemical surfactant compounds are the known sulfofatty acid methyl esters (fatty acid methyl ester sulfonates, MES) which are obtained by .alpha.-sulfonation of the methyl esters of fatty acids of vegetable and/or animal origin predominantly containing 10 to 20 carbon atoms in the fatty acid molecule and subsequent neutralization to water-soluble monosalts, more particularly the corresponding alkali metal salts. Ester cleavage thereof gives the corresponding .alpha.-sulfofatty acids or their disalts which, in the same way as mixtures of disalts and sulfofatty acid methyl ester monosalts, show important intrinsic washing and cleaning properties. However, comparable problems also arise in other classes of surfactants when attempts are made to produce the corresponding surfactant raw materials in dry form, cf. washing- and cleaning-active alkyl glycoside compounds. To obtain light-colored reaction products, their synthesis generally has to be completed by a bleaching step, for example using aqueous hydrogen peroxide, so that in this case, too, modern technology leads to the aqueous paste form of the surfactant. Water-containing alkyl glycoside pastes (APG pastes) are more vulnerable, for example, to hydrolysis or microbial contamination than corresponding dry products. In their case, too, simple drying by conventional methods presents considerable difficulties. Finally, however, even the drying of a water-containing paste of the alkali metal salts of washing-active soaps and/or alkylbenzene sulfonates (ABS pastes) can also present considerable problems.
The problem addressed by the present invention was to provide a simple alternative method of processing water-containing, more particularly paste-form, surfactant preparations to dry, more particularly free-flowing and concentrated surfactant granules.